1. Field of the Invention
The present invention relates to an external storage device that incorporates flash memory.
2. Description of the Related Art
From the past, there have been external storage devices that incorporate flash memory which is non-volatile semiconductor memory. With flash memory, data does not disappear even when the power is shut off, and it has features such as that it has a comparatively low price compared to EEPROM (Electrically Erasable Programmable ROM) which is another non-volatile memory. On the other hand, flash memory has structural limitations such as that data erasing is performed in block units, and that the number of block erases is limited. Specifically, by repeating erasing only of specific blocks, there is a marked decrease in life as memory. From this kind of flash memory feature, when using flash memory as an external storage device, a process of leveling the erase count for each block (in other words, the data rewrite count) is performed.
For example, in the No. WO99/21093-A, within the software, using an address conversion table (map) for linking the virtual address allocated as the storage area of specified data (also called the logical address) and the physical address of each block of the flash memory (also called the physical address), disclosed is a technology with which while attempting to level the block erase count, the physical block (physical address) of the flash memory corresponding to the virtual address for which data is written is specified.
However, with this kind of address conversion process, complex firmware software is required for converting the logical address and the physical address, and manufacturing of the firmware was complex and also took time for processing. Also, when this kind of process is executed using software, the processing by software increases, so in fact, significant time is used for processing.